Tissues Part 2 - Epithelial Tissue

your body needs order to function

Proper Epithelium: covers and lines your outer and inner body

Glandular Epithelium: forms your glands and secretes hormones and other substances

protects your whole body inside and out

all epithelial tissues are avascular

  • this means they are not associated with or supplied by blood vessles
  • instead they rely on blood supply from surrounding connective tissues

Shape and Layering:

  • shape of individual cells and the number of layers that they form in.

3 basic shapes:

  1. Squamous - flat (squished like fish sclaes)
  • fast absorption and disffusion, making thin membranes
  1. Cuboidal - about as tall as they are wide
  • absorb nutrients, produce secretions (Sweat)
  • circular nucleus
  1. Columnar cells - tall and thick
  • cushion underlying tissues
  • nuclei are stretched
  • they also absorb nutrients and produce secretions

squamous cells are flat so oxygen can move across them easier - see them in areas where transportation is important (ex. air sacs in your lungs)

Shape is very important in function

if they need to make mucus or hormones - need to be cubular or columnal - stomach lining is made of these

in places where you loose a lot of cells (like your mouth) you have squamous cells because they are cheaper to make (don't take as much time, energy and raw material as the others do)

Layering: Simple epithelium, stratified, pseudostratified

Simple Epithelium

  • one layer of cells

Stratified

  • multiple layers set on top of each other, like bricks

Pseudostratified

  • mostly just one layer combined of cells with different shapes and sizes

When classifying cells in a lab you talk both about it's shape and layering: ex. Simple Squamous epithelium

  • single layer of cells that are flat, scale-like

Stratified Cuboidal tissue

  • layers of cube shaped cells

Creates order among your organs:

These cells are polar:


Apical (upper) - exposed to the outside of your body or whatever internal cavity it is lining


Basal side - tightly attached to basement membrane

  • mostly collagen fibers that anchor it to the connective tissue

Semi-permeable

  • allowing some levels of absorption, filtration, and excretion of substances

Glands


two different types of glands: endocrine and exocrine

Endocrine: secrete hormones right into your bloodstream or to nearby cells

Exocrine: secrete their juices into tubes or ducts that lead to the outside of the body

  • ex. sweat, saliva, mucus, milk - fill into ducts where they will be secreted to the outside